In recent years, many numbers of young females prefer a slim body and often try weight loss by low calorie diets without physical activities. As a result, their body mass indexes (BMI) are average or low level but they have a rather high percent of body fat. They are called 'hiding obesity'. The first purpose of this study was to find out how many young females have poor body composition. Secondly, the effects of habitual exercise on young females' body composition and physical functions were investigated longitudinally. 284 young females (18-22yrs), all newly enrolled students at our college during the 3 years from 1997 to 1999 were measured for physique, body composition, anaerobic power (leg extension power) and aerobic power (PWCィイD275%HrmaxィエD2). Body composition was estimated by air displacement method. The results showed that the students requiring improvement in body composition amounted to 30% of all and most of them were hiding obesity. About 40% of all subjects had inferior leg power. The negative relationship between %fat and leg power was recognized.By having a weekly exercise class for half of one year, the mean value of their leg power increased significantly. The students who continually participated in a weekly exercise class for an additional half year showed more superior anaerobic and aerobic power. However, body composition did not improved. After that, the participation in a habitual combined training program consisting of aerobic exercise and stength training (1-2 times/week×12 weeks) caused significant improvements in not only physical strength but in body composition and serum components. The differences of the training effects between aerobic exercise program and combined exercise program (aerobic exercises plus strength training) were not clearly found.